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A method for suppressing the negative-mass instability in beams of particles with non-relativistic velocity is proposed and investigated theoretically. The method involves surrounding the beam with an inductive wall structure incorporating lumped-circuit inductors and does not rely on a velocity spread in the beam. The condition for stability of longitudinal oscillations of a given wavelength is v > v p , where v is the particle velocity and v p is the phase velocity of a wave with the same wavelength in the same structure, but with the beam replaced by a perfect conductor. A somewhat different structure consisting of a conducting ribbon wound in a helix around the beam is also analysed semi-quantitatively and shown to be effective in suppressing the instability.
Neil et al. (1967) studied this question.